The technology for manufacture of amorphous silicon photovoltaic cells has been developed over the past ten years. It is now known how to deposit electronic device quality amorphous silicon by compensating defects with hydrogen and/or fluorine. This high quality amorphous silicon may be deposited on thin flexible substrates such as a plastic or stainless steel. Large area amorphous silicon photovoltaic cells, consisting of one or more p-i-n structures formed from successively deposited layers, may be continuously produced on very long flexible substrates. See, for example, U.S. Pat. Nos. 4,400,409 and 4,410,558 to Izu, Cannella, and S. R. Ovshinsky, and U.S. Pat. No. 4,485,125 to Izu and H. C. Ovshinsky, the disclosures of which are incorporated herein by reference. These patents teach the continuous deposition of shingle and multiple p-i-n structures in sheet form, 25 cm. or more in width and hundreds of meters long. These sheets must be processed further to prepare working photovoltaic cells and interconnected arrays of such cells to produce operational photovoltaic panels.
A number of methods for defining separate photovoltaic cells from deposited sheet structures and for electrically interconnecting those cells have been proposed. Examples of such methods are disclosed in U.S. Pat. No. 4,419,530 to Nath, U.S. Pat. No. 4,443,652 to Izu, Nath and Holland, U.S. Pat. No. 4,485,264 to Izu and Nath and U.S. Pat. No. 4,514,579 to Hanak, the disclosures of which are incorporated herein by reference. In general, a transparent conductive oxide is deposited on the sheets to form one electrode of the cells and a metallic grid of conductors is deposited on the oxide to collect current from the oxide electrode efficiently. The conductive substrate forms a second electrode of the cells or interconnected array. By etching the semiconductor layers, individual cells may be defined and electrically connected in parallel. By interposing an insulator between the substrate and semiconductor body, the etching and grid patterns may be used to form series interconnected or series-parallel interconnected arrays of cells.
Alternatively, the sheet product of the continuous deposition process may be severed into strips, i.e. pieces having a longer length than width, that are interconnected mechanically and electrically into photovoltaic panels. When such panels are placed into service they are subjected to various environmental influences such as temperature variations and wind loading. Rigid interconnection of strips of cells has been proposed, but rigid panels may fail under environmental influences. Therefore, it is important that a panel formed of interconnected strips be flexible to avoid opening of electrical circuits in response to mechanical stress. While strips of amorphous silicon solar cells deposited on stainless steel are themselves flexible, at least around an axis perpendicular to their length, it is important that a panel assembled from strips be flexible both along its length and width.